This patent application claims priority to pending UK patent application Serial 1509525.0 filed Jun. 2, 2015 incorporated in its entirety herein by reference.
The present disclosure relates generally to an epoxy resin composition for manufacturing composite parts and, more particularly, to a fast curing epoxy resin composition suitable for use in high pressure resin transfer moulding applications.
It is well known that epoxy resin compositions or systems have a very valuable application in binding or impregnating various materials, such as glass fibres, carbon fibre mats or weaves, as well as other reinforcement materials. Manufacturing techniques for composite structures are also known and can vary. Practical conditions of moulding are fairly varied. In fact, there are different resin systems used for either high or low pressure moulding, for example, under partial vacuum to improve resin penetration into the reinforcement.
Resin transfer moulding (‘RTM’) is an increasingly common form of moulding wherein a catalysed, low viscosity resin composition is pumped into a mould under pressure, displacing the air at the edges, until the mould is filled. The mould can be packed with fibre preform or dry fibre reinforcement prior to resin injection. Once the mould is filled with resin, the resin cure cycle begins wherein the mould is heated to a temperature of about 100° C. or greater and the resin polymerizes to a rigid state.
In the automotive industry, high pressure resin transfer moulding (‘HP-RTM’) is one type of manufacturing solutions used by OEMs and their suppliers to manufacture automotive structures. Such equipment typically utilizes intelligent or computerized filling processes with closed loop control, as well as a high pressure metering system with sensor equipment for monitoring internal mould pressure. Using closed loop control, resin injection can be managed and controlled. After the mould is closed, a high compression force is applied and the resin is injected at a high pressure of about 30 to about 100 bar (atm), completing impregnation and curing the resin.
In order to meet manufacturing demands, the resin system used needs to have a cure time of about 10 minutes or less, preferably about 5 minutes or less at typical moulding temperatures of about 100° C. to about 130° C., and yield substantially fully cured composite parts having a resin glass transition temperature of greater than 130° C. without the use of a post cure or multifunctional resins. Resin systems used to manufacture such composite parts, particularly thermosetting polymer composite parts, prepared by a crosslinking reaction using an appropriate curing agent and epoxy resin, desirably have the following properties: (a) low viscosity suitable for HP-RTM (e.g., about 120 mPas or less at an injection temperature of about 120° C.); (b) fast cure reaction rate (e.g., about 5 minutes or less at 120° C. or about 3 minutes or less at 130° C.); (c) are substantially fully cured at the end of the reaction period (e.g., about 95 to 100% cured) and therefore do not require post-curing after moulding; and (d) have high resin Tg's (e.g., greater than about 120° C.) and high composite Tg's (e.g., greater than about 130° C.). One skilled in the art, however, recognizes that it is difficult to formulate epoxy resin compositions having all the properties desirable for manufacturing composite structures.
Different resin systems or formulations have been known and available for many years. These systems typically include one or more epoxy resins such as epoxy novolac resins and/or phenols such as those based on bisphenol-A (‘BPA’) and bisphenol-F (‘BPF’), among others. However, the epoxy resin used can affect different properties of the resin system, such as the mechanical properties and viscosity of the system.
The resin formulation also includes a hardener or curing agent such as polyethyleneimine, cycloaliphatic anhydride, dicyanamide (‘DICY’), imidazoles and amines such as diethylenetriamine (‘DETA’) and 1,3-bis(aminomethyl)cyclohexane (‘1,3-BAC’). The resin formulation may also require an accelerator or catalyst for accelerating the reactivity of the curing agent with the epoxy. However, the combinations of epoxies, hardeners and catalyst can negatively affect properties noted above needed to work in HP-RTM moulding manufacturing processes. Therefore, there is a need for fast curing epoxy compositions suitable for use in HP-RTM manufacturing processes that meets the manufacturing requirements of low viscosity, fast cure and high resin Tg's. These needs are addressed by the embodiments of the present invention as described below and defined by the claims that follow.